Bacteroides fragilis: current susceptibilities, mechanisms of drug resistance, and principles of antimicrobial therapy.

The Bacteroides fragilis group of organisms includes the most clinically important anaerobic bacteria. Optimal therapy of infections in which these organisms are involved includes adequate and timely surgical drainage of all collections, debridement of necrotic tissue, optimal nutritional support, and administration of appropriate empiric antibiotics to cover both the aerobic and anaerobic bacterial components of these mixed infections. Special attention must be paid to the B. fragilis group because of its high rate of resistance to many of the commonly used antibiotics. Of the currently available beta-lactam antibiotics, piperacillin has the lowest rate of resistance. Successful antimicrobial agents include clindamycin, chloramphenicol, and metronidazole plus an aminoglycoside. Piperacillin, cefoxitin, and moxalactam can be used with an aminoglycoside or alone if no resistant organisms are revealed on culture and susceptibility testing. Beta-lactam-based regimens are potentially less toxic and may be less costly than those that contain one or more non-beta-lactam antibiotics.